The art today knows fluid-regulating valves which can be shifted by small pneumatic, hydraulic or mechanical forces acting upon a shutter mechanism, thanks to the use of two relatively slidable plates with multiple apertures--usually designed as slits--that are mutually offset in a blocking position and are mutually aligned in an unblocking position. These sensitive valves, therefore, can be used either for direct flow regulation or as pilot valves for the control of associated flow-regulating valves. The precise design of their operating elements, however, makes them susceptible to various factors which may impair their function, among them possible blockages of fluid passages and inaccurate guidance of connecting members. When, for example, the valve body or housing includes a compartment bounded by a membrane or other resiliently biased member displaceable by fluid under pressure, that compartment ought to have a calibrated bleeding hole whose cross-sectional area determines the pressure required for opening or closing the valve. Such a bleeding hole is usually of rather small diameter and is therefore liable to become clogged by impurities or, if the controlling fluid is a hardenable liquid, by a residue of that liquid when the influx thereof has ceased.
In the case of a pilot valve controlled by a float measuring the level of a pool of liquid, e.g. in a tank intermittently fed with fresh liquid by way of that valve, the movement of the float is nonlinear when its support consists of a lever fulcrumed on the valve housing. The translation of the swing of that lever into a linear motion of a sliding shutter also creates problems which heretofore have made it difficult to utilize valves of the aforementioned sensitive type for this purpose. Moreover, when the connection between the float lever and the shutter includes a rod traversing adjoining walls of the tank and of the valve housing, it will be necessary to prevent leakage of liquid or of its vapors (e.g. when a volatile fluid such as a refrigerant is involved) into the valve housing when the latter must be opened for making its shutter mechanism accessible to an operator. The use of O-rings or similar sealing elements in the passage traversed by the rod should be avoided since their friction would reduce the efficiency of these sensitive valves; furthermore, a fluidtight seal will not be needed in normal operation when the fluid circulates in a closed system and the rod is disposed sufficiently above the highest liquid level in the tank. Conventional wisdom would dictate a way out of this difficulty by a draining of the system before an inspection or repair is to be carried out; this, however, is a rather inconvenient solution.
The need for such inspection or repair may also arise, with valves of this rather delicate nature, in systems in which the shifting of the slidable valve plate is controlled by means other than a float, e.g. by the aforementioned membrane. When the contact plane of the valve plates is perpendicular to a common axis of the entrance and exit ports lying on opposite sides of the shutter assembly, as shown in my above-identified copending application, access to the shutter can be had only through the port confronting same which therefore must be detachable from the associated conduit. In valves with shutter members displaceable against the flow direction for unblocking the fluid path, such as those marketed by Parker Hannifin Corporation of Broadview, Illinois, it is known (see their brochure titled Bulletin No. R/S 11582) to provide the valve housing with a neck having an axis inclined to that of the aligned ports at an acute angle and to close that neck with a lid in which an actuating rod is manually displaceable; a removal of the lid will provide access to the shutter but will also disconnect it from its actuating mechanism so that its operation under near-normal conditions could not be observed.